1. Field of the Invention
The present invention relates to a forked part structure of a double pipe with an inner pipe passing through an outer pipe, and a method of making the same.
2. Description of the Related Art
There is a double pipe provided with an inner pipe inside an outer pipe to form two flow paths. The use of such double pipes enables a simple and compact piping layout, and thus is favorable for a piping layout which has many restrictions. It is especially favorable for a piping layout of a vehicle air-conditioning system or the like, which is greatly restricted by a vehicle body structure or the like. The use of double pipes can also simplify assembly operations of an air-conditioning system, thereby reducing manufacturing costs.
Such double pipes need forked parts at their ends for connecting inner and outer pipes to different pipes. A forked part structure of a double pipe is disclosed in Japanese Published Unexamined Application No. S58-121394. In this double pipe forked part structure, an end portion of an outer pipe is expanded so that the end portion of the outer pipe is formed in a spectacle shape in cross section having two separate tubular portions. An inner pipe is inserted into and brazed to one tubular portion (inner pipe supporting portion), and a branch pipe is inserted into and brazed to the other tubular portion (branch pipe supporting portion).
In this structure, the inner pipe is brought into contact with or is likely to come into contact with the inner periphery of a main portion of the outer pipe. When the double pipe is placed on a vibrating body such as a vehicle, the inner or outer pipe vibrates, and can cause intermittent contact between the inner and outer pipes, producing a chattering sound.
Also, in this structure, it is probable that the gaps between the worked open end portion of the outer pipe and the inner pipe and the branch pipe inserted into the open end portion cannot be completely hermetically sealed by brazing. Especially when the two tubular portions are in close proximity, the joint margin of a joint formed between the two tubular portions is reduced, and the hermetic sealing at the end portion of the outer pipe can deteriorate.